As one of the goals of this project, we will investigate mechanisms by which certain polyunsaturated fatty acids, derived from "essential" fatty acids, (C20 and C22 acids) are incorporated into the phosphatidylethanolamine (PE) and lecithin of the hepatic cell membrane, both in vitro and in vivo. In the former instance, rat liver microsomes will be incubated with the appropriate radiolabeled precursors. After incorporation, microsomal lecithins or PE will be incubated with the appropriate radiolabeled precursors. After incorporation, microsomal lecithins or PE will be separated into molecular species by a combination of TLC and GLC techniques and the distribution of radioactivity determined. H3 and C14 radiolabeled lecithin fractions or fatty acids will be prepared from the microsomes in some instances or biosynthesized by the rat. The role of methionine and the sequential methylation pathway for the synthesis of plasma lipoprotein phospholipid will be studied in intact rats fed diets low in choline and methionine, then injected with C14H3-methionine. Distribution of radioactivity of the lecithin species will be determined at intervals after the injection in the plasma lipoproteins of these animals before and after supplementation with methionine or choline. In addition we hope to develop a deficiency of linolenic acid (n3) in rats, so that their docosahexaenoic acid (n3) is completely replaced with a pentaenoic acid (n6). Certain functional tests will be carried out in the deficient animals to see if docosahexaenoic acid in membrane lecithins can be replaced without disturbing essential function. These experiments will provide us with information on the function and metabolism of the polyunsaturated fatty acids in regard to their presence or absence on a particular lecithin species.